1. Field
The disclosure relates to electrolysis and more particularly electrolyzer apparatuses for the electrolytic splitting of water into hydrogen and oxygen gases.
2. Description of Related Art
Hydrogen gas is a commodity chemical that is used in numerous manufacturing processes, such as petroleum refining, fertilizer production, glass manufacturing and many others. Hydrogen gas can also be used for storing intermittent renewable energy, such as wind electrical energy and solar electrical energy. Electrolytic hydrogen and oxygen can be produced using nuclear-energy generated electricity and transported in pipe lines to distances remote from the nuclear reactor.
One commercial process for hydrogen production is steam reforming from hydrocarbons. However, steam reforming may utilize non-renewable sources of energy. Carbon monoxide and carbon dioxide may be by-products of fossil fuel-based methods for hydrogen production. There is considerable interest in finding non-polluting methods for large scale production of hydrogen, such as the electrolysis of water.
Solar photovoltaic and wind electricity generation are areas of technological activity in renewable energy. These technologies may suffer from an intermittency problem: solar and wind energies are not continuously available. Electrolysis of water may solve this problem by storing hydrogen and using it as a backup with fuel cells when solar and wind energies are not available. However, conventional electrolyzers may be complex structures that are labor-intensive to construct, metal-intensive in their use of materials and/or may not adequately lend themselves to modular scale-up for large-scale energy applications. Governments world-wide have spent more than $500 million dollars over the past 20 years in an effort to solve the problem of introducing advanced manufacturing techniques to expand the supply chain of electrolyzers for large-scale energy applications. Yet, the solution of this long-standing and important problem, the utilization of advanced manufacturing techniques for the practical large-scale production of inexpensive electrolyzers, may not have been achieved. Impediments to solving the problem are presented in the 2011 NREL/DOE Hydrogen and Fuel Cell Manufacturing R&D Workshop report, Aug. 11-12, 2011, Office of Energy Efficiency & Renewable Energy, Department of Energy, which is incorporated herein by reference in its entirety. The overall purpose of the workshop was to identify and prioritize: (1) barriers to the manufacture of hydrogen and fuel cell systems and components and (2) high-priority needs and R&D activities that government can support to overcome the barriers. Key results of the workshop report were plans for additional research on overcoming the barriers. The consensus vote of the workshop participants on the strategy for electrodes was how to apply ink directly to membranes. For the foregoing reasons, there remains a need for solving the long-standing problem of large-scale production of inexpensive electrolyzers that integrate advanced manufacturing techniques into the fabrication processes. The presentation materials of the 2012 Joint Fuel Cell Technologies and Advanced Manufacturing Office Webinar are incorporated herein by reference in their entirety. The 2011 report and 2012 Webinar materials are available as PDF files from the DOE Office of Energy Efficiency & Renewable Energy at http://www1.eere.energy.gov/hydrogenandfuelcells/wkshp_h2fc_manufacturing.html.
Electrolysis of water is a route to the production of hydrogen gas. Moreover, gaseous oxygen may be produced as a byproduct which may be a useful and valuable industrial and medical product. Electricity that is generated by renewable energy sources, such as wind, hydroelectric, solar and nuclear energy, can be used for electrolytic production of hydrogen and oxygen without the carbon dioxide and carbon monoxide that accompanies hydrogen production from fossil fuels. Patent references directed to electrolysis technology include, for example, U.S. Pat. Nos. 8,277,620, 8,273,495, 8,075,750, 8,075,749, 8,066,784, 7,964,068, 7,959,773, 7,951,274, 7,922,879, 7,906,006, 7,901,549, 7,892,6947, 704,353, 7,323,090, 7,132,190, 6,797,136, 6,582,571, 6,282,774, 5,728,485, 5,660,698, 5,606,488, 5,599,430, 5,171,644, 5,130,006, 5,080,963, 4,773,982, 4,636,291, 4,615,783, 4,541,911, 4,474,612, 4,432,859, 4,367,134, 4,311,577, 4,250,002, 4,206,030, 4,061,557, 4,014,776, 3,976,550, 3,855,104, 3,554,893, RE34,233, and U.S. Application Publication Nos. 2012/0193242, 2012/0149789, 2011/0243294 2010/0280347, 2010/0032221, 2009/0026089, 2008/0067078, 2004/0182695, 2003/0057088, 2002/0157958, 2002/0037422.
The electrolysis of water may involve the decomposition of water into oxygen and hydrogen gases by the action of an electric voltage applied to the water across electrodes of opposite polarity. Hydrogen may be produced at the negative electrode (cathode) and oxygen may be produced at the positive electrode (anode), as shown by the following reactions:Cathode (reduction): 4H+(aq)+4e−→2H2(g)Anode (oxidation): 2H2O(l)→O2(g)+4H+(aq)+4e−
In some electrolytic cells, a diaphragm that passes ions and impedes the passage of gases may separate cathode and anode compartments. The diaphragm may allow ionic conductivity between the compartments, while maintaining separation of the hydrogen and oxygen gases that are formed in their respective compartments. The anode reaction may remove electrons from water molecules under the influence of an applied external voltage. The removal of electrons may liberate oxygen and protons, H+, from the water. The protons may migrate across the diaphragm and combine with the removed electrons to form hydrogen. The combined net cathode and anode reactions may be: 2H2O→2H2+O2.